In a mobile communication system in which communication between a mobile communication network and a public telephone network is carried out, since subscribers move, there is no fixed exchange for the subscribers, called mobile stations. It is always necessary to follow and register the locations of mobile stations via control stations (in the network) at a higher rank than the radio base stations for determination of route selection, charge index, and a mobile visited area. That is called the location resistration of the mobile stations and a unit area of which the network manages as location information is called location registration area.
The location registration areas of individual mobile stations are registered in a home memory provided at a specific exchange station in the network. Further, for calling from the network side to a mobile station, a plurality of radio base stations simultaneously page all the mobile stations within the location registration area.
FIG. 9 shows a view for explaining one example of a conventional method for location registration of a mobile station. In the drawing, A and B are respectively location registration areas, and are assigned location registration codes LA and LB respectively. Z is a base station zone and there exists a radio base station at the center portion in the zone. A service area consisting of many base station zones Z each including a radio base station is divided into the location registration areas A and B. C shows an area boundary. The location registration codes LA and LB assigned to the location registration areas A and B are advised to mobile stations as broadcast signals by the radio base stations in the location registration areas A and B.
A mobile station compares the above location registration code LA or LB informed by the radio base stations with the location registration code storing by itself. Assuming that the mobile station moves into another location registration area, the comparison would not be successful. Accordingly, when the informed location registration code differs from the location registration code stored by the mobile station, the mobile station registers the informed location registration code to the home memory in the network side, and stores the informed new location registration code in its own memory. Therefore, the location where the mobile station exists and the location registration code (location registration area information) on the home memory coincide to each other.
However, the above conventional method of registering mobile communication locations has a drawback in that the number of location registrations and the traffic for the location registrations increase when a mobile station goes back and forth many times across the boundary C between the location registration areas A and B.
Further, the location registration is always carried out at the radio base stations near the boundary C, making the density of the location registrations high for these boundary stations. Still further, call request signals and location registration request signals are transmitted via the same upward directing control channels with random access so that in the zone at the peripheral of the location registration areas control signal traffic increases and signal collision probability is high. For that reason, the throughput of the control channel is reduced and subscriber capacity per each channel decreases so there arises a drawback which necessitates many control channels.
The present invention intends to overcome the above points, and an object of the present invention is to provide an improved method for registering a mobile station in which the traffic for the location registration in the respective radio zones is reduced, the concentration of the location registration traffic at the peripheral of the location registration area is reduced, and is averaged within the areas, and many subscribers are accomodated.